Back to EveryPatent.com
| United States Patent |
5,744,540
|
|
Baumstark
, et al.
|
April 28, 1998
|
Aqueous polymer emulsion
Abstract
An aqueous polymer emulsion is obtained by polymerizing first a monomer
composition 1 in a first polymerization stage and then a monomer
composition 2 in a polymerization stage 2, in each case by the free
radical aqueous emulsion polymerization method, one of the two monomer
compositions essentially comprising hard monomers and the other monomer
composition essentially comprising soft monomers, and, in addition to the
monomer compositions 1 and 2, nitrogen-containing adhesion-promoting
monomers being polymerized, at least 20 mol % of the total amount of the
adhesion-promoting monomers being polymerized in polymerization stage 1.
| Inventors:
|
Baumstark; Roland (Neustadt, DE);
Portugall; Michael (Wachenheim, DE);
Dersch; Rolf (Neustadt, DE);
Schweigger; Enrique (Ludwigshafen, DE)
|
| Assignee:
|
BASF Aktiengesellschaft (Ludwigshafen, DE)
|
| Appl. No.:
|
551489 |
| Filed:
|
November 1, 1995 |
| Current U.S. Class: |
524/558; 524/460; 524/555; 524/559; 524/561 |
| Intern'l Class: |
C08L 039/04 |
| Field of Search: |
524/558,559,561,460,555
|
References Cited
U.S. Patent Documents
| 3244655 | Apr., 1966 | Sullivan et al. | 524/460.
|
| 3454516 | Jul., 1969 | Victorius | 524/522.
|
| 4263193 | Apr., 1981 | Sakimoto et al. | 524/533.
|
| 4654397 | Mar., 1987 | Mueller-Mall | 524/460.
|
| 4994537 | Feb., 1991 | Craig et al. | 526/273.
|
| 5021469 | Jun., 1991 | Langerbeins et al. | 523/201.
|
| 5071902 | Dec., 1991 | Langerbeins et al. | 524/458.
|
| 5130367 | Jul., 1992 | Craig et al. | 524/819.
|
| 5185387 | Feb., 1993 | Klesse et al. | 523/201.
|
| 5468800 | Nov., 1995 | Folsch et al. | 524/458.
|
| Foreign Patent Documents |
| 0 184 091 | Jun., 1986 | EP.
| |
| 0 376 096 | Jul., 1990 | EP.
| |
| 0 379 892 | Aug., 1990 | EP.
| |
| 0 421 185 | Apr., 1991 | EP.
| |
| 0 429 207 | May., 1991 | EP.
| |
| 0 522 789 | Jan., 1993 | EP.
| |
| 0 609 793 | Aug., 1994 | EP.
| |
| 0 609 756 | Aug., 1994 | EP.
| |
| 0 623 659 | Nov., 1994 | EP.
| |
| 1 220 613 | Jul., 1966 | DE.
| |
| 34 18 524 | Nov., 1985 | DE.
| |
| 39 02 067 | Jul., 1990 | DE.
| |
| 43 34 178 | Apr., 1995 | DE.
| |
| WO 95/16720 | Jun., 1995 | WO.
| |
Primary Examiner: Jagannathan; Vasu
Assistant Examiner: Guarriello; John J.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt, P.C.
Claims
We claim:
1. An aqueous polymer emulsion obtained by polymerizing in a first
polymerization stage monomers 1 having at least one ethylenically
unsaturated group by free radical aqueous emulsion polymerization to a
conversion of at least 90% by weight, based on the monomers 1 to be
polymerized, and then polymerizing, in the presence of the product mixture
of the first polymerization stage, monomers 2 having at least one
ethylenically unsaturated group in a second free radical aqueous emulsion
polymerization stage, with the proviso that
a) the monomers 1 are such that their random copolymerization alone would
give a polymer 1 whose glass transition temperature tends to the limit
Tg.sup.1 with increasing molecular weight,
b) the monomers 2 are such that their random copolymerization alone would
give a polymer 2 whose glass transition temperature tends to the limit
Tg.sup.2 with increasing molecular weight,
c) the difference between Tg.sup.1 and Tg.sup.2 is at least 20.degree. C.,
d) in addition to the monomers of the monomers 1 and 2, at least one
adhesion-promoting monomer which differs from these monomers 1 and 2 and
contains at least one ethylenically unsaturated group and at least one
amino, ureido or N-heterocyclic group is polymerized in an amount of from
0.1 to 10% by weight, based on the total amount of the monomers to be
polymerized,
e) from 20 to 100 mol % of the total amount of the adhesion-promoting
monomers to be polymerized according to d) are polymerized in the first
polymerization stage and
f) the amount of the monomers of the polymer having the lower limit
Tg.sup.1 is from 40 to 90% by weight, based on the total amount of the
monomers 1 and 2.
2. An aqueous polymer emulsion as claimed in claim 1, wherein the
polymerization conversion of the first polymerization stage is at least
95% by weight, based on the monomers 1 to be polymerized.
3. An aqueous polymer emulsion as claimed in claim 1, wherein the
polymerization conversion of the first polymerization stage is at least
98% by weight, based on the monomers 1 to be polymerized.
4. An aqueous polymer emulsion as claimed in claim 1, wherein the amount of
the monomers of the polymer having the lower limit Tg.sup.i is from 60 to
80% by weight, based on the total amount of the monomers 1 and 2.
5. An aqueous polymer emulsion as claimed in claim 1, wherein the amount of
the monomers of the polymer having the lower limit Tg.sup.i is from 70 to
80% by weight, based on the total amount of the monomers 1 and 2.
6. An aqueous polymer emulsion as claimed in claim 1, wherein the
difference between Tg.sup.1 and Tg.sup.2 is from 20.degree. to 150.degree.
C.
7. An aqueous polymer emulsion as claimed in claim 1, wherein the
difference between Tg.sup.1 and Tg.sup.2 is from 60.degree. to 120.degree.
C.
8. An aqueous polymer emulsion as claimed in claim 1, wherein the lower of
the two limits Tg.sup.i is from -60.degree. to +35.degree. C.
9. An aqueous polymer emulsion as claimed in claim 1, wherein the lower of
the two limits Tg.sup.i is from -30.degree. to +35.degree. C.
10. An aqueous polymer emulsion as claimed in claim 1, wherein the lower of
the two limits Tg.sup.i is from -20.degree. to +20.degree. C.
11. An aqueous-polymer emulsion as claimed in claim 1, wherein the higher
of the two limits Tg.sup.i is from>50.degree. to 130.degree. C.
12. An aqueous polymer emulsion as claimed in claim 1, wherein the higher
of the two limits Tg.sup.i is from 60.degree. to 120.degree. C.
13. An aqueous polymer emulsion as claimed in claim 1, wherein the higher
of the two limits Tg.sup.i is from 95.degree. to 115.degree. C.
14. An aqueous polymer emulsion as claimed in claim 1, wherein the
polymerization stage 1 is of monomers resulting in a polymer having the
lower limit Tg.
15. An aqueous polymer emulsion as claimed in claim 1, wherein the monomers
1 and 2 are selected from the group consisting of n-butyl acrylate,
2-ethylhexyl acrylate, ethyl acrylate, methyl methacrylate, n-butyl
methacrylate, styrene, acrylonitrile, acrylic acid, methacrylic acid,
acrylamide, methacrylamide, hydroxyethyl acrylate, hydroxyethyl
methacrylate, n- hydroxypropyl acrylate, n-hydroxypropyl methacrylate,
acrylamidopropanesulfonic acid, vinylsulfonic acid and the alkali metal
salts thereof.
16. An aqueous polymer emulsion as claimed in claim 1, wherein the monomers
1 and 2 are selected from the group consisting of n-butyl acrylate,
n-butyl methacrylate, 2-ethylhexyl acrylate, methyl methacrylate, acrylic
acid, methacrylic acid, acrylamide and methacrylamide.
17. An aqueous polymer emulsion as claimed in claim 1, wherein the monomers
having the lower Tg.sup.i value comprises from 10 to 50% by weight, based
on the monomers whose homopolymers have Tg values above the lower Tg.sup.i
and the monomers of the polymer having the higher Tg.sup.i value
simultaneously comprises from 0 to 25% by weight, based on the monomers
whose homopolymers have Tg values below the higher Tg.sup.i.
18. An aqueous polymer emulsion as claimed in claim 1, whose minimum film
formation temperature without the addition of film formation assistants
is.ltoreq.30.degree. C.
19. An aqueous polymer emulsion as claimed in claim 1, which contains
ethyleneureaethyl methacrylate or N-(methacrylamidoethyl)ethyleneurea as
the adhesion-promoting monomer.
20. An aqueous polymer emulsion as claimed in claim 1, wherein from 30 to
100 mol % of the adhesion-promoting monomers are polymerized in
polymerization stage 1.
21. An aqueous polymer emulsion as claimed in claim 1, wherein from 40 to
100 mol % of the adhesion-promoting monomers are polymerized in
polymerization stage 1.
22. An aqueous polymer emulsion as claimed in claim 1, wherein from 50 to
100 mol % of the adhesion-promoting monomers are polymerized in
polymerization stage 1.
23. An aqueous polymer emulsion as claimed in claim 1, wherein from 40 to
60 mol % of the adhesion-promoting monomers are polymerized in
polymerization stage 1.
24. An aqueous polymer emulsion as claimed in claim 1, whose solids content
is.gtoreq.40% by volume.
25. An aqueous polymer emulsion as claimed in claim 1, whose solids content
is.gtoreq.50% by volume.
26. An aqueous polymer emulsion as claimed in claim 1, whose solids content
is from 40 to 70% by volume.
27. An aqueous polymer emulsion as claimed in claim 1, whose weight average
diameter of the disperse polymer particles is from 40 to 300 nm.
28. An aqueous polymer emulsion as claimed in claim 1, whose weight average
diameter of the disperse polymer particles is from 50 to 150 nm.
29. An aqueous polymer emulsion as claimed in claim 1, whose weight average
diameter of the disperse polymer particles is from 50 to 100 nm.
30. An aqueous polymer emulsion as claimed in claim 1, whose nonuniformity
of the polymer particle diameter distribution is from 1 to 5.
31. An aqueous polymer emulsion as claimed in claim 1, whose nonuniformity
of the polymer particle diameter distribution is from 1 to 2.
32. An aqueous polymer emulsion as claimed in claim 1, wherein the
polymerization temperature in both polymerization stages is from
60.degree. to 90.degree. C.
33. An aqueous polymer emulsion as claimed in claim 1, wherein the pH of
the aqueous dispersing medium is buffered to a value of from 3 to 6 over
the entire duration of the free radical aqueous emulsion polymerization.
34. An aqueous polymer emulsion as claimed in claim 1, which additionally
contains at least one compound having at least two unprotected and/or
reversibly protected aldehyde groups.
35. An aqueous polymer emulsion as claimed in claim 1, which contains
glyoxal or glutardialdehyde as the polyaldehydic compound.
36. A polymer which is contained in a polymer emulsion as claimed in claim
1.
37. A method of adhering, coating or impregnating a material, comprising
applying to the material an aqueous polymer emulsion as claimed in claim
1.
38. An aqueous color formulation containing an aqueous polymer emulsion as
claimed in claim 1 as a binder.
39. An aqueous coating, impregnating or adhesive formulation, containing an
aqueous polymer emulsion as claimed in claim 1 as a binder.
40. A substrate which is coated, impregnated or adhesively bonded with an
aqueous formulation which contains an aqueous polymer emulsion as claimed
in claim 1.
41. A process for the preparation of an aqueous polymer emulsion according
to claim 1, comprising polymerizing in a first polymerization stage
monomers 1 having at least one ethylenically unsaturated group by free
radical aqueous emulsion polymerization to a conversion of at least 90% by
weight, based on the monomers 1 to be polymerized in the first
polymerization stage and monomers 2 having at least one ethylenically
unsaturated group is then polymerized in the presence of the product
mixture of the first polymerization stage by free radical aqueous emulsion
polymerization in a second polymerization stage, wherein
a) the monomers 1 are such that their random copolymerization alone would
give a polymer 1 whose glass transition temperature tends to the limit
Tg.sup.1 with increasing molecular weight,
b) the monomers 2 are such that their random copolymerization alone would
give a polymer 2 whose glass transition temperature tends to the limit
Tg.sup.2 with increasing molecular weight,
c) the difference between Tg.sup.1 and Tg.sup.2 is at least 20.degree. C.,
d) in addition to the monomers of the monomers 1 and 2, at least one
adhesion-promoting monomer which differs from these monomers and contains
at least one ethylenically unsaturated group and at least one amino,
ureido or N-heterocyclic group is polymerized in an amount of from 0.1 to
10% by weight, based on the total amount of the monomers to be
polymerized,
e) from 20 to 100 mol % of the total amount of the adhesion promoting
monomers to be polymerized according to d) are polymerized in the first
polymerization stage and
f) the amount of the monomers of the polymer having the lower limit
Tg.sup.1 is from 40 to 90% by weight, based on the total amount of the
monomers 1 and 2.
42. An aqueous polymer emulsion as claimed in claim 1, whose minimum film
formation temperature without the addition of film formation assistants
is.ltoreq.10.degree. C.
43. An aqueous polymer emulsion as claimed in claim 1, wherein both the
monomers 1 and the monomers 2 are metered continuously into the
polymerization vessel in the course of the polymerization stages 1 and 2
as a corresponding monomer mixture which may be preemulsified in an
aqueous medium, and the adhesion-promoting monomers which are to be
polymerized in the particular polymerization stage are fed to the
polymerization vessel after being mixed in the corresponding monomer
mixture 1 and 2.
44. An aqueous polymer emulsion as claimed in claim 43, wherein the
continuous monomer feed is carried out in such a way that the
polymerization conversion of the monomers already added to the
polymerization vessel is.gtoreq.90% by weight at any time after the
beginning of the polymerization.
45. An aqueous polymer emulsion as claimed in claim 43, wherein the
continuous monomer feed is carried out in such a way that the
polymerization conversion of the monomers already added to the
polymerization vessel is.ltoreq.95% by weight at any time after the
beginning of the polymerization.
46. An aqueous polymer emulsion as claimed in claim 43, wherein the
continuous monomer feed is carried out in such a way that the
polymerization conversion of the monomers already added to the
polymerization vessel is.ltoreq.98% by weight at any time after the
beginning of the polymerization.
Description
FIELD AND SUMMARY OF THE INVENTION
The present invention relates to an aqueous polymer emulsion obtainable by
polymerizing a composition 1 of compounds (monomers) having at least one
ethylenically unsaturated group by the free radical aqueous emulsion
polymerization method to a conversion of at least 90, preferably at least
95, particularly preferably at least 98%, by weight, based on the monomer
composition 1 to be polymerized, (polymerization stage 1) and then
polymerizing, in the presence of the product mixture of polymerization
stage 1, a composition 2 of compounds (monomers) having at least one
ethylenically unsaturated group by the free radical aqueous emulsion
polymerization method (polymerization stage 2), with the proviso that
a) the composition 1 is such that random copolymerization of the
composition 1 alone would give a polymer 1 whose glass transition
temperature tends to the limit Tg.sup.1 with increasing molecular weight,
b) the composition 2 is such that random copolymerization of the
composition 2 alone would give a polymer 2 whose glass transition
temperature tends to the limit Tg.sup.2 with increasing molecular weight,
c) the difference between Tg.sup.1 and Tg.sup.2 is at least 20.degree. C.,
d) in addition to the monomers of the compositions 1 and 2, at least one
adhesion-promoting monomer which differs from these monomers and contains
at least one ethylenically unsaturated group and the element nitrogen is
polymerized in an amount of from 0.1 to 10, frequently from 0.5 to 5,
preferably from 1 to 3%, by weight, based on the total amount of the
monomers to be polymerized,
e) from 20 to 100 mol % of the total amount of the adhesion-promoting
monomers to be polymerized according to d) are polymerized in
polymerization stage 1 and
f) the amount of that composition i which is assigned the lower limit
Tg.sup.i is from 40 to 90% by weight, based on the total amount of the
compositions 1 and 2.
The present invention furthermore relates to processes for the preparation
of novel aqueous polymer emulsions and their use for coating, adhesive
bonding, sealing and impregnating, their use as binders for coating
materials and in particular glazes being preferred.
Aqueous polymer emulsions are fluid systems which contain polymer particles
distributed in stable disperse form as the disperse phase in the aqueous
dispersing medium. The diameter of the polymer particles is in general
mainly from 0.01 to 5 .mu.m, frequently mainly from 0.01 to 1 .mu.m.
As in the case of polymer solutions on evaporation of the solvent, aqueous
polymer emulsions have the ability to form transparent polymer films on
evaporation of the aqueous dispersing medium, and it is for this reason
that said emulsions are widely used as binders, for example for surface
coatings or materials for coating leather.
In contrast to the polymer solution, however, the type of disperse polymer
and the temperature at which film formation takes place determine whether
an aqueous polymer emulsion forms a cohesive transparent film or a
brittle, opaque pulverizable layer after evaporation of the water. The
lowest temperature at which a transparent film without cracks is just
formed is to be referred to below as the minimum film formation
temperature (MFT) of the relevant aqueous polymer emulsion. No film
formation takes place below the MFT (cf. Ullmanns Encyklopadie der
technischen Chemie, Vol. 19, 4th edition, Verlag Chemie, Weinheim (1980),
page 17).
It is generally known that aqueous emulsions of polymers which essentially
contain only polymerized monomers whose homopolymers have low glass
transition temperatures Tg (in this publication, Tg is the limit of the
glass transition temperature to which, according to G. Kanig,
Kolloid-Zeitschrift & Zeitschrift fur Polymere, Vol. 190, page 1, equation
1, the glass transition temperature tends with increasing molecular
weight, determined by the DSC method (Differential Scanning Calorimetry,
20.degree. C./min, midpoint); the Tg values for the homopolymers of most
monomers are known and are stated, for example, in Ullmann's Encyclopedia
of Industrial Chemistry, VCH Weinheim, 1992, fifth edition, Vol. A21, page
169; other sources of glass transition temperatures of homopolymers are,
for example, J. Brandrup, E. H. Immergut, Polymer Handbook, 1st edition,
J. Wiley, N.Y. 1966, 2nd edition, J. Wiley, N.Y. 1975, and 3rd edition, J.
Wiley, N.Y., 1989) (ie. soft monomers) are as a rule also capable of
forming polymer films at appropriately low temperatures. However, a
disadvantage of the resulting films is that they are too soft and too
tacky for many applications. This is a disadvantage in that such films
readily become soiled, for example through the adhesion of dust. In
particular, coatings produced from such films usually also have a low
blocking temperature. The latter is the temperature at which such coatings
stick together when they are brought into contact with one another under a
predetermined contact pressure for some time. Above the blocking
temperature, the coatings adhere to one another and can no longer be
separated from one another without the coatings being damaged. Blocking
can also occur if the coatings are not tacky to the touch. The blocking
temperature is important particularly when substrates provided with
coatings based on aqueous polymer emulsions are to be stacked one on top
of the other or freshly painted windows are to be closed. When the
coatings are brought into contact below the blocking temperature, they can
be separated from one another again essentially without the use of force
and without being damaged.
It is also generally known that aqueous emulsions of polymers which contain
essentially only polymerized hard monomers (monomers whose homopolymers
have a high glass transition temperature Tg) generally have a high
blocking temperature. However, the disadvantage of these aqueous polymer
emulsions is that they also require a high temperature for film formation.
It is true that to a certain extent the MFT and blocking temperature (BT)
can be adapted to the desired application by copolymerization of hard and
soft monomers or by mixing aqueous emulsions of hard polymers with aqueous
emulsions of soft polymers or by adding plasticizers. However, the
disadvantage of these adaptation measures is that they generally change
the MFT and BT to the same extent, ie. they usually increase or decrease
the BT and the MFT to a comparable extent.
In terms of application, however, it is desirable to have adaptation
measures which are capable of increasing the temperature difference
between MFT and BT.
EP-A 184 091, EP-A 376 096, German Published Application DAS 1,220,613,
U.S. Pat. No. 3,454,516, EP-A 609 756 and EP-A 379 892 disclose that the
abovementioned aim can be essentially realized by spatially combining the
free radical aqueous emulsion polymerization in two successive stages, one
of the two stages mainly comprising soft polymers and the other stage
mainly comprising hard monomers. Surprisingly, the sequence of the two
stages, ie. whether the hard stage is polymerized first and then the soft
stage or vice versa, tends to play a minor role. For example, EP-A 379 892
describes the sequence hard/soft, whereas EP-A 184 091 uses the sequence
soft/hard. Both EP-A 184 091 and EP-A 379 892 furthermore describe the
polymerization of a nitrogen-containing adhesion-promoting monomer in the
second polymerization stage in order to increase the adhesion of the films
of such aqueous polymer emulsions to many materials, such as wood, metal,
minerals, paper, textiles and plastic, but in particular to old surface
coatings based on drying oils and/or alkyd resins, and to reduce the
sensitivity of the adhesion to the effect of humidity and moisture
(increased wet adhesion). The placing of the wet adhesion monomers in the
second polymerization stage is based on the idea that this results in the
production of disperse polymer particles which have the adhesion-promoting
monomers localized in particular on their surface, which should promote
their adhesion-improving interaction with the substrate to be coated.
EP-A 609 756 relates both to the sequence hard/soft and to the sequence
soft/hard. With this polymerization method, EP-A 609 756 associates the
idea of forming both hard and soft regions within the disperse polymer
particles. Furthermore, EP-A 609 756 like-wise recommends the
copolymerization of nitrogen-containing adhesion-promoting monomers for
improving the wet adhesion. With regard to the placing of the
adhesion-promoting monomers, EP-A 609 756 states that they could be placed
both exclusively in the soft or exclusively in the hard regions of the
polymer particles and simultaneously in the hard and the soft regions of
the polymer particles (page 1, lines 20 to 22). In all embodiments of EP-A
609 756, the realization of this placing is achieved by virtue of the fact
that the total amount of the adhesion-promoting monomers is polymerized as
part of the second polymerization stage, ie. EP-A 609 756 also starts from
the idea of preferred localization of the adhesion-promoting monomers on
the surface of the disperse polymer particles. This is also true of DE-A
39 02 067 and EP-A 609 793. The prior art thus provides aqueous polymer
emulsions which are satisfactory with respect to the difference between
MFT and BT and with regard to the wet adhesion, but the disadvantage of
the prior art aqueous polymer emulsions is that their films are
unsatisfactory simultaneously with regard to elongation at break and with
regard to gloss. An increased elongation at break is important in that the
substrates to be coated generally have cracks and/or fissures which become
larger or smaller under the action of temperature fluctuations owing to
the fact that the coefficients of thermal expansion of the substrates are
non-zero, with the result that extension of their coating may occur. This
is true in particular when the substrate to be coated is wood. In the
latter, humidity fluctuations in particular result in extension processes.
It is an object of the present invention to provide aqueous polymer
emulsions which do not have these disadvantages of the prior art aqueous
polymer emulsions.
We have found that this object is achieved by the aqueous polymer emulsions
defined at the outset, whose films surprisingly have a significantly
higher gloss and a significantly higher elongation at break than the prior
art films most closely resembling them, without there being any
significant reduction in the wet adhesion as a result.
DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION
In principle, the novel procedure can advantageously be applied to all
hard/soft or soft/hard sequences mentioned in evaluating the prior art.
These are in particular the sequences of EP-A 609 756, EP-A 379 892, EP-A
184 091, EP-A 376 096, German Published Application DAS 1,220,613 and U.S.
Pat. No. 3,454,516.
However, those novel aqueous polymer emulsions in which the amount of that
monomer composition i which is assigned the lower limit Tg.sup.i is from
50 to 90, better from 60 to 80, preferably from 70 to 80%, by weight,
based on the total amount of the compositions 1 and 2, are advantageous.
The magnitude of the difference between Tg.sup.1 and Tg.sup.2 may be at
least 30.degree., 40.degree., 50.degree., 60.degree., 70.degree.,
80.degree., 90.degree., 100.degree., 120.degree., 150.degree. C. or more
and as a rule is therefore from 20.degree. to 150.degree. C. With regard
to applications, the magnitude of the difference between Tg.sup.1 and
Tg.sup.2 is advantageously from 60.degree. to 120.degree. C. or from
40.degree. to 80.degree. C.
It is also advantageous if the lower limit Tg.sup.i is from -60.degree. to
35.degree. C., preferably from -30.degree. to +35.degree. C., very
particularly preferably from -20.degree. to +20.degree. C.
Correspondingly, it proves advantageous if the higher of the two limits
Tg.sup.1 is from>50.degree. to 130.degree. C., preferably from 60.degree.
to 120.degree. C., very particularly preferably from 95.degree. to
115.degree. C.
In the case of a specified Tg.sup.i for the monomer composition i, the
monomer composition i can be established in a simple manner by means of
the Fox equation. According to Fox (T. G. Fox, Bull. Am. Phys. Soc. (Ser.
II) 1, (1956), 123, and Ullmanns Encyklopadie der technischen Chemie,
Verlag Chemie, Weinheim, 1980, Vol. 19, 4th Edition, page 18) a good
approximation for the glass transition temperature of random copolymers is
##EQU1##
where X.sup.1, X.sup.2, . . ., X.sup.n are the mass fractions of the
monomers 1, 2, . . ., n and Tg.sup.1, Tg.sup.2, . . ., Tg.sup.n are the
glass transition temperatures, in degrees Kelvin, of the polymers composed
only of one of the monomers 1, 2 . . ., or n.
A random copolymerisation of a monomer composition i can be realized
experimentally by polymerizing a corresponding monomer mixture by aqueous
emulsion free radical polymerization by the feed method. In this
procedure, the monomer mixture is preemulsified in the aqueous phase and
is fed into the polymerization vessel at the rate of consumption with the
addition of initiators so that the polymerization conversion of the
monomers present in the polymerization vessel is.gtoreq.99% by weight.
Preferred initiators are sodium peroxodisulfate, and the polymerization
temperature is usually from 60.degree. to 90.degree. C. The polymerization
pressure may be atm, depending on the monomers. The dispersants used may
be.gtoreq.1 the substances recommended in this publication for the
preparation of the novel aqueous polymer emulsions. The molecular weight
can be established in a manner known per se by the concommitant use of
molecular weight regulators (eg. mercaptans) and/or by means of the
amounts of initiator used. In the absence of molecular weight regulators
and using from 0.1 to 2% by weight, based on the amount of monomers, of
polymerization initiator, an aqueous polymer emulsion whose glass
transition temperature corresponds to the limiting Tg can be obtained.
Preferred novel aqueous polymer emulsions are those in which the
polymerization stage 1 relates to the monomer composition which is
assigned the lower limit Tg.sup.i, ie. according to the invention the
sequence soft/hard is preferred.
Monoethylenically unsaturated monomers capable of free radical
polymerization, such as styrene, a-methylstyrene, o-chlorostyrene or
vinyltoluenes, esters of vinyl alcohol with monocarboxylic acids of 1 to
18 carbon atoms, such as vinyl acetate, vinyl propionate, vinyl
n-butyrate, vinyl laurate and vinyl stearate, esters of
.alpha.,.beta.-monoethylenically unsaturated mono- and dicarboxylic acids
of, preferably, 3 to 6 carbon atoms, in particular acrylic acid,
methacrylic acid, maleic acid, fumaric acid and itaconic acid, with
alkanols of in general 1 to 12, preferably 1 to 8, in particular 1 to 4,
carbon atoms, especially methyl, ethyl, n-butyl, isobutyl, tert-butyl,
2-ethylhexyl, norbonyl and isobornyl acrylate and methacrylate, dimethyl
maleate or n-butyl maleate, nitriles of .alpha.,.beta.-monoethylenically
unsaturated carboxylic acids, such as acrylonitrile and methacrylonitrile,
and conjugated C.sub.4 -C.sub.8 -dienes, such as 1,3-butadiene and
isoprene, are particularly suitable for producing the monomer compositions
1 and 2. Commercially available monomers VEOVA.RTM. 9-11 (VEOVA X is a
tradename of Shell and relates to vinyl esters (of carboxylic acids which
are also referred to as Versatic.RTM. X acids) of the general formula
##STR1##
where R.sup.1, R.sup.2 and R.sup.3 are alkyl radicals whose total number
of carbon atoms (R.sup.1 +R.sup.2 +R.sup.3) is equal to X minus 2, are
also important).
The main part of the monomer compositions 1 and 2 is generally chosen from
the abovementioned monomers and altogether accounts for more than 50% by
weight, based on the particular monomer composition. Monomers which, when
polymerized alone, usually give homopolymers which have high water
solubility are usually contained in both monomer compositions only in
modifying amounts. These are usually less than 50, as a rule less than 20,
preferably from 0.1 to 10, frequently also from 0.1 to 5%, by weight,
based on the total amount of the particular monomer composition. Examples
of such monomers are .alpha.,.beta.-monoethylenically unsaturated ono- and
dicarboxylic acids of 3 to 6 carbon atoms and amides thereof, for example
acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid,
acrylamide and methacrylamide, as well as vinylsulfonic acid,
acrylamidopropanesulfonic acid and water-soluble salts of the
abovementioned acids.
Both the monomer composition 1 and the monomer composition 2 preferably
contain from 0.1 to 5% by weight, based on the particular monomer
composition i, of the abovementioned modifying monomers whose homopolymers
have high water solubility.
In addition to the abovementioned monomers, the monomer compositions 1 and
2 may contain minor amounts, as a rule from 0.01 to 5% by weight, based on
the particular monomer composition i, of monomers which effect
crosslinking of the polymer chains within the individual disperse polymer
particles. Particularly suitable in this respect are monomers having two
or more nonconjugated ethylenically unsaturated groups, for example the
diesters of dihydric alcohols with .alpha.,.beta.-monoethylenically
unsaturated monocarboxylic acids, among which in turn the acrylates and
methacrylates are preferably used. Alkylene glycol diacrylates and
dimethacrylates, such as ethylene glycol diacrylate, 1,3-butylene glycol
diacrylate, 1,4-butylene glycol diacrylate and propylene glycol
diacrylate, may be mentioned by way of example.
Divinylbenzene, vinyl methacrylate, vinyl acrylate, allyl methacrylate,
allyl acrylate, diallyl maleate, diallyl fumarate, methylenebisacrylamide,
cyclopentadienyl acrylate and triallyl cyanurate are also suitable. Of
course, both the monomer composition 1 and the monomer composition 2 may
simultaneously comprise such precrosslinking monomers. However, it is
sometimes also advantageous if only one of the two monomer compositions
contains such precrosslinking agents. Frequently, they are only part of
the first or of the second polymerization stage. Their exclusive use in
the hard polymerization stage is particularly advantageous. However, they
may also be present only in the soft polymerization stage.
It is often advantageous if at least one of the two monomer compositions 1
and 2 or both of them comprises or comprise minor amounts, usually from
0.5 to 5% by weight, based on the particular monomer composition i, of
monomers which do not effect crosslinking until during film formation.
Examples are carbonyl-containing monomers, such as acrolein, methacrolein,
diacetoneacrylamide, diacetonemethacrylamide and vinylaceto acetate. The
abovementioned monomers result in postcrosslinking, for example, when the
aqueous polymer emulsion simultaneously contains an appropriate added
amount of a polyamine compound. Particularly suitable compounds of this
type are the dihydrazides of aliphatic dicarboxylic acids of 2 to 10
carbon atoms. Examples of these are oxalic dihydrazide, malonic
dihydrazide, succinic dihydrazide, glutaric dihydrazide, adipic
dihydrazide and sebacic dihydrazide.
Another monomer which produces postcrosslinking is, for example,
2-acetoacetoxyethyl methacrylate (alone or in combination with polyamines
or polyaldehydes, such as glyoxal).
Other polymer building blocks which are suitable for postcrosslinking are
those which contain hydrolyzable organosilicon bonds. Examples are the
copolymerizable monomers methacryloyloxypropyltrimethoxysilane and
vinyltrimethoxysilane. Further suitable polymer building blocks of a
corresponding type are described in DE-A 43 41 260. If the disperse
polymer particles have carboxyl groups, postcrosslinking can also be
effected by adding metal salts having polyvalent cations (for example Mg,
Ca, Zn or Zr salts).
Epoxy-, hydroxyl- and/or N-alkylol-containing monomers, for example
glycidyl acrylate, N-methylolacrylamide and -methacrylamide and monoesters
of dihydric alcohols with .alpha.,.beta.-monoethylenically unsaturated
carboxylic acids of 3 to 6 carbon atoms, such as hydroxyethyl,
hydroxy-n-propyl or hydroxy-n-butyl acrylate and methacrylate, are also
suitable for postcrosslinking.
If the novel aqueous polymer emulsions comprise systems which effect
precrosslinking and/or postcrosslinking, the glass transition temperatures
Tg.sup.1 and Tg.sup.2 to be assigned in accordance with the definition to
the monomer compositions 1 and 2 are understood as meaning the glass
transition temperatures to be determined in the absence of these
crosslinking components present only in minor amounts. As a rule, the
precrosslinking and/or postcrosslinking have an advantageous effect on the
initial blocking temperature (directly after film formation) and the final
blocking temperature (after several days).
The monomer compositions 1 and 2 are preferably chosen, in the manner
described above, exclusively from the following monomers: n-butyl
acrylate, 2-ethylhexyl acrylate, ethyl acrylate, methyl ethacrylate,
n-butyl methacrylate, styrene, acrylonitrile, acrylic acid, methacrylic
acid, acrylamide, methacrylamide, hydroxyethyl acrylate, hydroxyethyl
methacrylate, n-hydroxypropyl acrylate, n-hydroxypropyl methacrylate,
acrylamidopropanesulfonic acid and vinylsulfonic acid and the alkali metal
salts thereof.
Particularly preferably, the monomer compositions 1 and 2 are chosen, in
the manner described above, exclusively from the following monomers:
n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, n-butyl
methacrylate, acrylic acid, methacrylic acid, acrylamide and
methacrylamide.
In general, it proves advantageous if, on the one hand, the monomer
composition i having the lower Tg.sup.i value comprises from 10 to 50% by
weight, based on the monomer composition i, of monomers whose homopolymers
have Tg values above the lower Tg.sup.i and, on the other hand, the
monomer composition i having the higher Tg.sup.i value simultaneously
comprises from 0 to 25% by weight, based on the monomer composition i, of
monomers whose homopolymers have Tg values below the higher Tg.sup.i. In
general, advantageous novel aqueous polymer emulsions are those whose MFT
is.ltoreq.30.degree. C., preferably.ltoreq.10.degree. C., without the
addition of film formation assistants.
Particularly suitable nitrogen-containing adhesion-promoting monomers are
monomers which are capable of free radical polymerization and have at
least one amino, ureido or N-heterocyclic group.
A large number of such suitable adhesion-promoting monomers are described
in EP-B 421 185, EP-B 379 892, page 3, EP-A 609 756, page 2, DE-A 43 34
178, DE-A 3 902 067, pages 3 and 4, and the references cited in these
publications.
Examples are aminoethyl acrylate and methacrylate,
dimethylaminoethylacrylate and methacrylate, diethylaminoethyl acrylate
and methacrylate, dimethylaminopropyl acrylate and methacrylate,
3-dimethylamino-2,2-dimethylprop-1-yl acrylate and methacrylate,
2-N-morpholinoethyl acrylate and methacrylate, 2-N-piperidinoethyl
acrylate and methacrylate, N-(3-dimethylaminopropyl)acrylamide and
-methacrylamide, N-dimethylaminoethylacrylamide and -methacrylamide,
N-diethylaminoethylacrylamide and -methacrylamide,
N-(4-morpholinomethyl)acrylamide and -methacrylamide, vinylimidazole and
monoethylenically unsaturated derivatives of ethyleneurea, such as
N-(2-acryloyloxyethyl)ethyleneurea,
N-(.beta.-acrylamidoethyl)ethyleneurea, N-2-(allylcarbamato)aminoethylimid
azolidinone (WAM IV from Air Products and Chemicals),
N-(3-allyloxy-2-hydroxypropyl)aminoethylethyleneurea (Sipomer.RTM. WAM
from Alcolac), N-vinylethyleneurea, N-vinyloxyethylethyleneurea,
N-methacryloyloxyacetoxyethylethyleneurea,
N-(acrylamidomethylene)ethyleneurea,
N-(methacrylamidomethylene)-ethyleneurea and the particularly preferred
N-(2-methacryloyloxyethyl)ethyleneurea.quadbond.1-(2-methacryloyloxyethyl)
imidazolin-2-one.quadbond.ureidoethyl
methacrylate.quadbond.ethyleneureaethyl methacrylate (Plex.RTM. 6844-0
from Rohm GmbH) and
N-(methacrylamidoethyl)ethyleneurea.quadbond.N-(.beta.-methacrylamidoethyl
)ethyleneurea (Sipomer WAM II from Rhone-Poulenc). Further particularly
suitable ureido monomers are stated in a review article by R. W. Kreis, A.
M. Sherman, Developments in Ureido Functional Monomer for Promoting Wet
Adhesion in Latex Paints, Water-Borne and Higher Solids Coating Symposium
of Feb. 3 to 5, 1988, New Orleans, La.
Preferably from 30 to 100 mol % or from 40 to 100 mol % or from 50 to 100
mol % of the nitrogen-containing adhesion-promoting monomer to be
polymerized according to the definition are polymerized in polymerization
stage 1. With regard to an optimum balance of all desired properties,
particularly advantageous novel aqueous polymer emulsions are obtained
when from 40 to 60 mol % of the total amount of adhesion-promoting
monomers to be polymerized according to the definition are copolymerized
in polymerization stage 1.
The novel aqueous polymer emulsions are preferably produced with a solids
content of.gtoreq.40, advantageously.gtoreq.50%, by volume, based on the
total aqueous polymer emulsion. As a rule, the advantageous solids content
for applications is from 40 to 70% by volume.
Regarding the desired performance characteristics, it is advantageous if
the weight average diameter of the disperse polymer particles is from 40
to 300 nm. Particularly advantageous weight average polymer particle
diameters are from 50 to 150 nm or from 50 to 120 nm. Unless the dynamic
viscosity of the novel aqueous polymer emulsion plays the decisive role,
the distribution of the polymer particle diameters is preferably narrow.
The nonuniformity of the polymer particle diameter distribution should be
less than 5, preferably less than 2. It is a ratio of weight average to
number average polymer particle diameter.
The preparation of the novel aqueous polymer emulsions is carried out
according to the product by process definition of the subject according to
the invention, as stated at the outset, ie. by the free radical aqueous
emulsion polymerization method in the presence of dispersants and free
radical polymerization initiators.
The ratio of the aqueous phase to the total amount of the monomers used in
both stages is chosen according to the desired solids content of the
aqueous polymer emulsion to be prepared.
The monomer composition 1 may be initially taken in its entirety as a
corresponding monomer mixture in the form of an aqueous monomer emulsion
in the polymerization vessel or some or all of said monomer composition 1
may be metered into said vessel in the course of the polymerization stage
1 as an emulsion in an aqueous medium or in anhydrous form. The monomer
composition 1 can of course be realized only over the total polymerization
stage 1 when considered in an integral manner. In this case, a monomer
mixture whose composition changes as a function of time and corresponds to
the monomer composition 1 only when considered in an integral manner is
added to the polymerization vessel. This latter procedure is less
preferable. After the end of the polymerization stage 1, the monomer
composition 2 can be added in a corresponding manner to the polymerization
vessel, all at once or partly or in total in the course of the
polymerization stage 2, as an emulsion in an aqueous medium or in
anhydrous form. The novel adhesion-promoting monomers to be polymerized
are preferably mixed into the other monomers or the emulsions thereof and
introduced in this form into the polymerization vessel. Thus, monomer
mixtures whose composition is constant as a function of time are
preferably added to the polymerization vessel over the particular
polymerization stage, in both polymerization stages. The latter is
advantageously carried out in such a way that the polymerization
conversion of the monomers already added to the polymerization vessel
is.gtoreq.90, preferably.gtoreq.95, particularly preferably.gtoreq.98%, by
weight at any time after the beginning of the polymerization.
In both stages, the polymerization is initiated by conventional free
radical initiators. Suitable initiators are all those which are capable of
initiating a free radical aqueous emulsion polymerization. These may be
both peroxides, for example alkali metal or ammonium peroxodisulfate, and
azo compounds, such as azobisisobutylronitrile or 4,4'-azobiscyanovaleric
acid. Combined systems which are composed of at least one organic reducing
agent and at least one peroxide and/or hydroperoxide, for example
tert-butyl hydroperoxide and the sodium salt of hydroxymethanesulfinic
acid or hydrogen peroxide and ascorbic acid, and very particularly
preferably combined systems which furthermore contain a small amount of a
metal compound which is soluble in the polymerization medium and whose
metallic component may occur in a plurality of valency states, for example
ascorbic acid/iron(II) sulfate/hydrogen peroxide, are also advantageously
used, the sodium salt of hydroxymethanesulfinic acid, sodium sulfite or
sodium bisulfite also frequently being used instead of ascorbic acid and
alkali metal peroxodisulfate and/or ammonium peroxodisulfate often being
used instead of hydrogen peroxide. Instead of a water-soluble iron(II)
salt, a V salt or a combination of water-soluble Fe/V salts is also
frequently used. The amount of the free radical initiator systems used is
preferably from 0.1 to 2% by weight, based on the total amount of the
monomers to be polymerized. Depending on their type, the polymerization
initiators may be initially taken all at once in the polymerization vessel
in a manner known per se to a person skilled in the art or may be added
continuously to said vessel at the rate at which they are consumed, ie.
according to the progress of the polymerization.
The polymerization pressure and polymerization temperature are of fairly
minor importance. In general, both polymerization stages are carried out
at from room temperature to 100.degree. C., preferably from 50.degree. to
95.degree. C., particularly preferably from 60.degree. to 90.degree. C.
Reduced or superatmospheric pressure may be used, so that the
polymerization temperature may also exceed 100.degree. C. and may be up to
130.degree. C. or more. Readily volatile monomers, such as ethylene or
butadiene, are preferably polymerized under superatmospheric pressure. For
regulating the pH of the polymerization medium, pH buffers, such as
NaHCO.sub.3, Na.sub.2 CO.sub.3, sodium acetate or Na.sub.2 P.sub.2
O.sub.5, are preferably added during the novel free radical aqueous
emulsion polymerization. pH buffers are advantageously incorporated into
the aqueous monomer emulsions to be introduced. Buffering is preferably
effected to a pH of from 3 to 6. This measure results in the novel aqueous
polymer emulsions having greater freedom from coagulum and specks
(microcoagulum). Alternatively to the use of buffers, the aqueous monomer
emulsion to be fed in may also be partly neutralized by means of a strong
base (eg. NaOH) to a pH of from 3 to 6 before being added. The
ready-to-use final pH of the novel aqueous polymer emulsions is generally
increased to above 7, preferably up to 9, by adding bases, such as
ammonia, alkali metal hydroxide (NaOH, KOH), alkali metal oxide, alkaline
earth metal oxide, alkaline earth metal hydroxide (Ca(OH).sub.2), ZnO,
metal carbonates, metal bicarbonates or amines, such as
2-amino-2-methyl-1-propanol, ethanolamine, diethanolamine, triethylamine,
morpholine, N,N-dimethylethanolamine or
2-dimethylamino-2-methyl-1-propanol.
To improve the reproducibility and establish defined particle diameters,
the polymer particle formation phase and polymer particle growth phase are
advantageously decoupled from one another in a manner known per se to a
person skilled in the art by initially taking a defined amount of a
preformed aqueous polymer emulsion (a seed latex) in the polymerization
vessel or preforming such an emulsion in situ in said vessel. The amount
of dispersant added in the further course of the free radical aqueous
emulsion polymerization is as a rule such that the critical micelle
formation concentration is not exceeded and formation of new polymer
particles is thus avoided. If a broad particle diameter distribution is
desirable for producing highly concentrated aqueous novel polymer
emulsions, seed latex is generally added to the polymerization vessel
additionally during the free radical aqueous emulsion polymerization in a
manner known per se. Molecular weight regulators, for example mercaptans,
may of course concommitantly be used in the novel free radical aqueous
emulsion polymerization. This generally facilitates the film formation
(lower MFT) and thus enhances the gloss level. However, the polymerization
is frequently carried out in the absence of said regulators. As in the
case of free radical polymerization methods generally, the novel method
can be used, in a manner known to a person skilled in the art, both under
an inert gas atmosphere (eg. N.sub.2, Ar) and under a nitrogen-containing
atmosphere (eg. air).
Suitable dispersants which ensure in particular the stability of the novel
aqueous polymer emulsion are both the protective colloids usually used for
carrying out the free radical aqueous emulsion polymerization and
emulsifiers.
Suitable protective colloids are, for example, polyvinyl alcohols,
cellulose derivatives or vinylpyrrolidone-containing copolymers. A
detailed description of further suitable protective colloids is given in
Houben-Weyl, Methoden der organischen Chemie, Volume XIV/1,
Makromolekulare Stoffe, Georg-Thieme-Verlag, Stuttgart, 1961, pages 411 to
420. Mixtures of emulsifiers and/or protective colloids may of course also
be used. Preferably used dispersants are exclusively emulsifiers with
relative molecular weights, in contrast to the protective colloids, of
usually less than 2000, preferably less than 1000. They may be anionic,
cationic or nonionic. Where mixtures of surfactants are used, the
individual components must of course be compatible with one another, which
in case of doubt can be tested by means of a few preliminary experiments.
In general, anionic emulsifiers are compatible with one another and with
nonionic emulsifiers. The same applies to cationic emulsifiers, whereas
anionic and cationic emulsifiers are generally incompatible with one
another. Useful emulsifiers are, for example, ethoxylated mono-, di- and
trialkylphenols (degree of ethoxylation: 3 to 100, alkyl radical: C.sub.4
to C.sub.12), ethoxylated fatty alcohols (degree of ethoxylation: 3 to
100, preferably 6 to 50, alkyl radical: C.sub.6 to C.sub.20) and alkali
metal and ammonium salts of alkylsulfates (alkyl radical: C.sub.8 to
C.sub.18), of sulfuric half-esters of ethoxylated alkanols (degree of
ethoxylation: 1 to 70, in particular 2 to 10, alkyl radical: C.sub.10 to
C.sub.18) and of ethoxylated alkylphenols (degree of ethoxylation: 3 to
100, preferably 6 to 50, alkyl radical: C.sub.4 to C.sub.18) and alkali
metal and ammonium salts of alkanesulfonic acids (alkyl radical: C.sub.10
to C.sub.18) and of alkylarylsulfonic acids (alkyl radical: C.sub.9 to
C.sub.18). Further suitable emulsifiers, such as sulfosuccinates, are
described in Houben-Weyl, Methoden der organischen Chemie, Volume XIV/1,
Makromolekulare Stoffe, Georg-Thieme Verlag, Stuttgart, 1961, pages 192 to
208.
Compounds of the general formula I
##STR2##
where A.sup.1 and A.sup.2 are each hydrogen or C.sub.4 -C.sub.24 -alkyl
and are not simultaneously hydrogen and X and Y may be alkali metal ions
and/or ammonium ions, have also proven to be suitable surfactants. In the
formula I, A.sup.1 and A.sup.2 are each preferably linear or branched
alkyl of 6 to 18, in particular 6, 12 or 16, carbon atoms or hydrogen, and
A.sup.1 and A.sup.2 are not both simultaneously hydrogen. X and Y are
preferably sodium, potassium or ammonium ions, sodium being particularly
preferred. Compounds I in which X and Y are sodium, A.sup.1 is a branched
alkyl radical of 12 carbon atoms and A.sup.2 is hydrogen or A.sup.1 are
particularly advantageous. Industrial mixtures which contain from 50 to
90% by weight of the monoalkylated product, for example Dowfax.RTM. 2A1
(trademark of Dow Chemical Company), are frequently used. The compounds I
are preferably used as dispersants in the novel process alone or,
particularly preferably, as a mixture with ethoxylated fatty alcohols
(degree of ethoxylation: 3 to 50, alkyl radical: C.sub.8 to C.sub.36). The
compounds I are generally known, for example from U.S. Pat. No. 4,269,749,
and are commercially available.
As a rule, the amount of dispersant used is from 0.5 to 6, preferably from
1 to 5, particularly preferably from 2 to 4%, by weight, based on the
monomers to be subjected to free radical polymerization.
Remarkably, the internal strength of films of the novel aqueous polymer
emulsions can be increased particularly where the disperse polymer, owing
to the copolymerization of adhesion-promoting monomers, contains at least
one group of the general formula II
##STR3##
where X is O or S and
B.sup.1 and B.sup.2 are each hydrogen or C.sub.1 -C.sub.5 -alkyl or both
together form a bridging C.sub.2 -C.sub.4 -alkylene group which may be
unsubstituted or monosubstituted or disubstituted by C.sub.1 -C.sub.4
-alkoxy and/or hydroxyl,
by the simultaneous presence of at least one chemical compound having at
least two unprotected and/or reversibly protected aldehyde groups in the
novel aqueous polymer emulsion, the ratio of the total molar amount of
groups II contained in the aqueous polymer formulation to the total molar
amount of abovementioned unprotected and/or reversibly protected aldehyde
groups contained in the aqueous polymer emulsion being from 0.1:1 to 10:1.
Remarkably, such novel aqueous polymer emulsions have a satisfactory shelf
life. It is also remarkable that the wet adhesion is essentially not
adversely affected by the postcrosslinking. Moreover, films of novel
aqueous polymer emulsions postcrosslinked in this way have higher water
resistance and less tendency to blooming. The abovementioned molar ratio
is preferably 1:0.1 to 1:2, particularly preferably from 1:0.1 to 1:1,
very particularly preferably from 1:0.5 to 1:1. Groups of the general
formula II which are particularly preferred in the abovementioned sense
and particularly advantageous aldehydic compounds are described in EP-A
609 793 and DE-A 43 34 178. Glyoxal and glutardialdehyde are particularly
advantageous aldehydic compounds.
Novel aqueous polymer emulsions are typically used in the area of aqueous
coating materials, in particular those which are free of organic solvents,
where the film formed from the aqueous polymer emulsion adhesively bonds
to the substrate.
This area includes in particular surface coatings for interior and exterior
applications in the building trade.
Other examples are industrial coating materials, in particular where
elevated temperatures cannot be realized or are difficult to realize in
their application. Examples of such coatings are finishes, wash primers,
insulations and heat-sealable adhesive layers. The novel aqueous polymer
emulsions are also suitable for the consolidation of sheet-like fibrous
structures. While films of the pure plastics emulsions are suitable for
the last-mentioned applications, they are generally pigmented and/or mixed
with fillers for the coating sector. Conventional formulations may be used
here, the advantages of low MFT, high BT, good gloss and high elongation
at break always being displayed. Glazes, finishes, silk gloss coats, gloss
coats and high gloss coats and materials for coating leather may be
mentioned in particular here. Examples of particularly suitable substrates
are wood, leather, metal, plastic and mineral materials. The novel
polymers are also suitable as additives in mineral binders, in particular
those based on cement.
Especially in the case of interior applications, it is necessary for the
novel aqueous polymer emulsions to be substantially free of residual
monomers and organic solvents. This can be achieved in a manner known per
se, for example by removal by distillation (in particular steam
distillation) or by stripping with an inert gas. Free radical
postpolymerization methods can of course also be used (in particular with
the action of redox initiator systems), as stated, for example, in DE-A 44
35 423, DE-A 44 19 518 and DE-A 44 35 422 or cited as prior art.
The polymers dispersed in the novel aqueous polymer emulsions may be
isolated, for example, by careful spray drying or by coagulation in a
manner known per se and subsequent thorough washing. Where they are not
directly redispersible as such in an aqueous medium, they generally
dissolve in organic solvents. These solutions can be transferred to an
aqueous medium and transformed into a stable dispersion of the polymer in
the aqueous medium with removal of the organic solvent by distillation and
addition of a dispersant.
EXAMPLES
A) Preparation of novel aqueous polymer emulsions D1 to D6 and of
comparative dispersions VD1 to VD4
A mixture of
200 g of water,
25 g of a 20% strength by weight aqueous solution of ethoxylated fatty
alcohol (alkyl radical: C.sub.16 /C.sub.8 mixture, average degree of
ethoxylation: 18)=emulsifier solution 2,
60 g of a 15% strength by weight aqueous solution of sodium
laurylsulfate=emulsifier solution 1,
10 g of feed 1 and
10 g of feed 3
was initially taken in a polymerization vessel and heated to 85.degree. C.
in the course of 10 minutes. Stirring was carried out for 10 minutes at
85.degree. C., after which the remaining amount of feed 1 was continuously
metered into the polymerization vessel in the course of 1.5 hours while
maintaining the temperature of 85.degree. C. Beginning simultaneously with
the remaining amount of feed 1, the remaining amount of feed 3 was
continuously fed into the polymerization vessel in the course of 2 hours.
After the end of feed 1, feed 2 was continuously fed into the
polymerization vessel in the course of 30 minutes while further
maintaining the temperature of 85.degree. C. The polymerization mixture
was then stirred for a further 2 hours at 85.degree. C. Thereafter, the
mixture was cooled to 25.degree. C., 6 ml of concentrated aqueous ammonia
solution were added and the emulsion was filtered through a filter having
a mesh size of 250 .mu.m.
Feed 1
90+X g of water,
250 g of n-butyl acrylate,
125 g of methyl methacrylate,
6.4 g of acrylic acid,
4.3 g of a 50% strength by weight aqueous solution of acrylamide,
0.5 g Na.sub.4 P.sub.2 O.sub.7
2.1 g of emulsifier solution 1,
22.5 g of emulsifier solution 2
X g of ureidoethyl methacrylate.
Feed 2
30+Y g of water,
125 g of methyl methacrylate,
Y g of ureidoethyl methacrylate,
1.1 g of acrylic acid,
0.7 g of a 50% strength by weight aqueous acrylamide solution,
6.7 g of emulsifier solution 1
3.75 g of emulsifier solution 2.
Feed 3
2.5 g of sodium peroxodisulfate dissolved in 100 g of water.
Table 1 below shows the specifically used values for X and Y, characterizes
the resulting aqueous polymer emulsions and indicates the performance
characteristics obtained with coating formulations prepared using these
aqueous polymer emulsions.
TABLE 1
__________________________________________________________________________
Elong-
Solids
Blocking Wet
ation at
Gloss
Emul- content (%
resistance (after
MFT
adhe-
break
(mean value/peak
sion
X (g)
y (g)
by weight)
1 h/after 24 h)
(.degree.C.)
sion
(%) value)
__________________________________________________________________________
VD1 -- -- 49.2 0/0 <6 6 519 18/18
VD2 -- 5 49.7 0.5/0.5
8 3.5
295 67/67
VD3 -- 7.5
50.1 0/0 7 3 224 64/65
VD4 -- 10 49.5 0/1 8 3 236 61/63
D1 5 -- 50.7 0/0 <6 4 478 73/73
D2 7.5
-- 50.1 0/0.5
<6 4 458 73/73
D3 10 -- 49.5 0/1 <6 2 434 72/72
D4 5 5 49.6 0/0 <6 3 310 68/69
D5 7.5
2.5
49.8 0/0 <6 2 425 72/73
D6 2.5
7.5
49.9 0/0.5
10 3.5
295 69/70
__________________________________________________________________________
Description of the test methods used for determining the performance
characteristics shown in Table 1
a) Formulation of a protective wood glase and determination of the blocking
resistance
Protective wood glazes were formulated from the aqueous polymer emulsions
VD1 to VD4 and D1 to D6 as follows:
100 g of water,
2 g of 30% strength by weight aqueous solution of the ammonium salt of a
medium molecular weight polyacrylic acid (pigment disperser A from BASF
AG),
50 g of propylene glycol,
16 g of Syloid.RTM. ED5 (dulling agent from Grace GmbH, Worms),
5 g of Mergal.RTM. BCM (fungicide/blue stain inhibitor combination from
Riedel-de-Haen AG, Seelze),
3 g of Agitan.RTM. 232 (antifoam from Muzing Chemie GmbH, Heilbronn),
19 g of butylglycol,
5 g of Lusolvan.RTM. FBH (film formation assistant from BASF AG),
700 g of aqueous polymer emulsion,
30 g of water,
______________________________________
65 g Luconyl .RTM. yellow and
pigment preparations from
5 g Luconyl .RTM. red BASF AG.
______________________________________
To test the blocking resistance of the prepared protective wood glazes,
square test specimens having an edge length of 2 cm were cut from Leneta
films (sintered PVC films containing carbon black, from Schwegmann GmbH in
D-53501 Grafschaft Gelsdorf) coated with the glazes in a wet thickness of
100 .mu.m, after drying for 24 hours at 23.degree. C. and 50% relative
humidity, and the coated sides of pairs of said test specimens were
pressed against one another over a period of 1 hour and 24 hours under an
applied mass of 5 kg at 60.degree. C. The test pieces were cooled to
23.degree. C. and then separated from one another, and the force required
to do so and the resulting film characteristics were evaluated on the
basis of the following scale of values:
0: test pieces fall apart under their own weight and the films remain
intact;
1: test pieces can be separated from one another without significant use of
force but the films remain intact;
2: slight force has to be applied to separate the test pieces but the films
remain intact;
3: greater force has to be applied to separate the test pieces, and small
holes and cracks are produced in the films;
4: considerable force has to be applied to separate the test pieces, and
larger holes and cracks are produced in the films;
5: test pieces can be separated from one another only with the application
of very considerable force, and the films are considerably damaged during
separation.
b) Determination of the minimum film formation temperature (MFT)
The minimum film formation temperature was determined for the pure aqueous
polymer emulsion according to Ullmanns Encyklopadie der technischen
Chemie, Vol. 19, Verlag Chemie, Weinheim (1980), page 17. The measuring
instrument used was a film formation bench (=metal plate to which a
temperature gradient is applied). The film produced had a thickness of 500
.mu.m when wet. The MFT is the temperature at which cracks began to appear
in the film.
c) Formulation of a silk gloss coating material and determination of the
wet adhesion
Silk gloss coating materials were formulated from the aqueous polymer
emulsions VD1 to VD4 and D1 to D6 as follows:
89 g of water,
6 g of 25% strength by weight aqueous solution of the sodium salt of a
copolymer of maleic acid and diisobutylene (dispersant for pigments and
fillers),
2 g of Parmetol.RTM. A23 (preservative),
9 g of Natrosol.RTM. 250 HR (4% strength by weight aqueous thickener
solution based on hydroxyethylcellulose),
32 g of propylene glycol,
10 g of butyldiglycol,
4 g of Agitan.RTM. 702 (antifoam),
210 g of Kronos.RTM. RHD-2 (finely divided TiO.sub.2 pigment),
106 g of talc SE Micro (filler),
10 g of Collacral.RTM. PU75 (Polyurethane associated thickener),
13 g of butyldiglycol,
5 g of Kristallol.RTM. K60 (hydrocarbon mixture as film formation
assistant) and
504 g of aqueous polymer emulsion.
To test the wet adhesion of the silk gloss coating materials formulated as
described above to alkyd resin coating, a high-gloss solvent-containing
commercial alkyd resin coating material was first applied to Leneta film
in a wet coat thickness of 120 .mu.m and was dried for one day at room
temperature and for 7 days at 50.degree. C. in a through-circulation
dryer. The alkyd resin primer coat was cooled to 23.degree. C., after
which the particular silk gloss coating material was applied to it in a
wet coat thickness of 200 .mu.m and dried for 3 days at 23.degree. C,/65%
relative humidity. The surface was then damaged by cutting with a knife
and, in order to test the wet adhesion of the top coat to the alkyd resin
primer coat, the films prepared as described were subjected to a plurality
of successive frost-thaw cycles. In the course of one frost-thaw cycle, the
coated films were first stored for 8 hours in water at 23.degree. C., then
kept for 16 hours at -20.degree. C. and then placed in water for 10
minutes at 23.degree. C. After the fifth frost-thaw cycle, the adhesion of
the topcoat to the primer coat was tested at 23.degree. C. at the incision
point and was rated according to the following scale of values:
1=excellent
2=good
3=completely satisfactory
4=satisfactory
5=poor
6=insufficient
d) Determination of the elongation at break (%)
The elongation at break was determined on the basis of DIN 53455 and DIN
53504. The measured values stated are mean values of 5 measurements on 5
test specimens.
For the production of the test specimens, a mixture of
60 g of aqueous polymer emulsion,
4 g of butylglycol and
56 g of water
was prepared in each case and samples were converted into films (0.5 mm dry
thickness) in a silicone mold over a period of 7 days at 23.degree. C. at
50% relative humidity. After removal of the film from the silicone mold,
the test specimens required for carrying out the tensile test were punched
out of said films.
The test specimen format used was the dumbbell format described in DIN
53504 (cf. 2.4.11.6) as standard bar S2. The thickness of the samples was
checked with the thickness measuring apparatus according to DIN 53370,
having a circular tracing form of 10 mm diameter.
The test specimens were clamped in the clamps of a tensile test machine and
torn at a take-off speed of 200 mm/min. The elongation at break is the
elongation at the instant of tearing. It is based on 23.degree. C. It is
expressed as (L-L.sub.0 /L.sub.o).times.100 (%), where
L.sub.o is the original measured length and
L is the measured length on tearing.
e) Carrying out gloss measurements
Coats of the aqueous polymer emulsions were applied in a wet thickness of
200 .mu.m to Leneta film measuring 16 cm.times.8 cm. After film formation
had continued for 24 hours at 23.degree. C. and 50% relative humidity, the
gloss of the film was determined at 23.degree. C. and angle of observation
of 60.degree. using a Micro-TRI gloss reflectometer from BYK-Gardner at 3
measuring points randomly selected on the film surface. The mean value of
the 3 determinations and the maximum value are stated. An increasing gloss
value reflects increasing gloss.
B) Postcrosslinking of novel aqueous polymer emulsions with glyoxal
The novel aqueous polymer emulsion D7 was prepared by the general
preparation method stated in A), the initially taken mixture and feeds
having the following composition:
Initially taken mixture:
380 g of water,
120 g of emulsifier solution 1,
25 g of emulsifier solution 2,
20 g feed 1,
30 g feed 3.
Feed 1
200 g of water,
420 g of n-butyl acrylate,
330 g of methyl methacrylate,
10 g of ureidoethyl methacrylate,
7.5 g of acrylic acid,
8.5 g of 50% strength by weight aqueous solution of acrylamide,
1 g Na.sub.4 P.sub.2 O.sub.7
4.3 g of emulsifier solution 1 and
37.5 g of emulsifier solution 2.
Feed 2
70 g of water,
250 g of methyl methacrylate,
10 g of ureidoethyl methacrylate,
7.5 g of acrylic acid,
1.5 g of 50% strength by weight aqueous solution of acrylamide,
13.3 g of emulsifier solution 1 and
37.5 g of emulsifier solution 2.
Feed 3
200 g of water and
1.5 g of sodium peroxodisulfate.
Zg of a 40% strength by weight aqueous glyoxal solution were stirred into
500 ml of each of the resulting aqueous polymer emulsions D7. The aqueous
polymer emulsions obtained were tested as follows for water absorption and
resistance to blooming:
a) Determination of the water absorption (WA)
About 500 .mu.m thick polymer films were produced from the
glyoxal-containing aqueous polymer emulsions after dilution with water to
a solids content of 25% by weight, by converting a defined amount of
aqueous polymer emulsion into a film over a period of 5 days at 23.degree.
C. and 50% relative humidity in a silicone pan.
The polymer films were then removed from the silicone pan, and sheet-like
square film pieces (about 4 cm.sup.2) were punched out. These were placed
in 100 ml of demineralized water for 24 hours at 23.degree. C.
The water absorption of the sample pieces was determined gravimetrically.
It is stated in Table 2 in % by weight, based on the initial weight of the
test specimen.
b) Determination of the resistance to blooming (RB)
The glyoxal-containing aqueous polymer formulations were applied by means
of a knife coater to a glass sheet to give a layer which was 200 .mu.m
thick when wet, and were converted into a film over a period of 24 hours
at 23.degree. C. and 50% relative humidity. The glass sheets coated in
this manner were placed vertically, at 23.degree. C. for 4 hours, in a
trough filled with demineralized water. The sheets were then removed from
the trough and the films were checked visually for blooming and blister
formation.
The results obtained are shown in Table 2.
TABLE 2
______________________________________
Molar
ratio of
ureido/
aldehyde WA (% by
Amount D7
Z groups weight)
RB
______________________________________
500 ml -- -- 28.2 many small
blisters, very
great opacity
500 ml 0.43 1:0.25 22.3 many small
blisters, great
opacity
500 ml 0.86 1:0.5 20.1 no blister
formation, slight
opacity
500 ml 1.72 1:1 18.9 no blister
formation, no
opacity
(transparent firm)
______________________________________
C) Preparation of further novel aqueous polymer emulsions and determination
of performance characteristics
In all cases, the preparation was carried out according to the general
preparation method in A. In the case of the emulsions D15 and D16, the
total feed time (=feed time of feed 1+feed time of feed 2) was likewise 2
hours, but the feed times of feeds 1 and 2 were chosen so that their ratio
corresponded to the weight ratio of the particular total amount of monomers
contained in feeds 1 and 2. The determinations for the performance
characteristics were also carried out as in A). The composition of the
initially taken mixture and of the feeds and the performance
characteristics are shown in Table 3. The following abbreviations were
used there:
BA=n-butyl acrylate,
MMA=methyl methacrylate,
UMA=ureidoethyl methacrylate,
AA=acrylic acid,
MAA=methacrylic acid
AM=50% strength by weight aqueous acrylamide solution,
GS=40% strength by weight aqueous glyoxal solution,
BDA=1,4-butylene glycol diacrylate,
NaPS=sodium peroxodisulfate,
DAAM=50% strength by weight aqueous diacetoneacrylamide solution,
ADDH=adipic dihydrazide,
E1=aqueous emulsifier solution 1,
E2=aqueous emulsifier solution 2,
F1=feed 1,
F2=feed 2.
The amounts are stated in each case in g.
TABLE 3
__________________________________________________________________________
Initially
taken
mixture
D8 D9 D10
D11
D12 D13
D14
D15
D16
D17 D18
D19
__________________________________________________________________________
Water 200
200
200
200
200 200
200
200
200
200 200
200
E1 60 60 60 60 60 60 66.7
60 60 60 60 60
E2 12.5
12.5
12.5
12.5
12.5
12.5
-- 12.5
12.5
12.5
25 25
F1 10 10 10 10 10 10 10 10 10 10 10 10
F2 15 15 15 15 15 15 15 15 15 15 10 10
Feed 1
Water 95 95 95 95 95 95 95 95 80 95 88 85
BA 250
250
250
250
250 250
250
250
250
250 250
250
MMA 125
125
125
125
125 125
125
100
75 125 125
125
UMA 5 5 5 5 5 5 5 5 5 5 3.8
2.5
AA 6.4
3.8
3.8
3.8
3.8 3.8
3.8
3.8
3.8
5MAS
6.4
6.4
AM 4.3
4.3
4.3
4.3
4.3 4.3
4.3
4.3
4.3
4.3 4.3
4.3
E1 2.1
2.1
2.1
2.1
2.1 2.1
6.7
2.1
2.1
2.1 2.1
2.1
E2 18.8
18.8
18.8
18.8
18.8
18.8
-- 18.8
18.8
18.8
22.5
22.5
1,5
15 g
BDA
DAAM
Feed 2
Water 35 35 35 35 35 35 35 35 55 35 40 40
MMA 125
125
125
125
125 125
125
150
175
125 125
125
UMA 5 5 5 5 5 5 5 5 5 5 3.8
2.5
AA 1.1
3.8
3.8
3.8
3.8 3.8
3.8
3.8
3.8
5MAS
1.1
1.1
AM 0.8
0.8
0.8
0.8
0.8 0.8
0.8
0.8
0.8
0.8 0.8
0.8
E1 6.7
6.7
6.7
6.7
6.7 6.7
6.7
6.7
6.7
6.7 6.7
6.7
E2 18.8
18.8
18.8
18.8
18.8
18.8
-- 18.8
18.8
18.8
18.8
18.8
Feed 3
Water 100
100
100
100
100 100
100
100
100
100 100
100
NaPS 1.5
1.5
1.5
1.5
1.5 0.8
1.5
1.5
1.5
1.5 2.5
2.5
MFT (.degree.C.)
<6 <6 7 <6 5 <6 11 <6 <6 <6 <6 <6
Gloss (M/S)
73/74
70/72
70/70
72/72
71/71
61/62
70/71
67/70
64/70
-- 71/73
73/74
Elongation
312
268
278
236
189 246
186
232
216
221 378
408
at break
(%)
Blocking
resistance
1 h 0 0 0 0 0 0 0 1 1 0 0 0
24 h 0 0 0 0 0 0 0 1 0.5
0 0 0
Wet 1 2 4 3 4 3 1 4 4 3 3 4
adhesion
__________________________________________________________________________
Top